Number of free polybends with n cells.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =8a(5) =15a(6) =25a(7) =45a(8) =74a(9) =135a(10) =233a(11) =414a(12) =715a(13) =1279a(14) =2248a(15) =3952a(16) =6924a(17) =12279a(18) =21623a(19) =37895a(20) =66551a(21) =117379a(22) =206576a(23) =361376a(24) =634301a(25) =1115258a(26) =1959444a(27) =3424197a(28) =6003124a(29) =10532541